In mechanical machinery which includes relatively movable parts, it is desired that the lifetime of the various elements of the machine be limited substantially only by metal fatigue and not by wear and tear. In order to attain this long life, it is normally required to apply lubricant between relatively moving elements of the machine. The resupply of lubricant must occur at regular intervals in order to prevent any direct metal-to-metal contact which would cause rapid wear and tear. It is known in the art to increase the period of time between intervals of relubrication by providing a relatively large grease reservoir. However, it has been found that only a relatively small proportion of the lubricant in these grease reservoirs actually ever reaches the points of greatest friction, i.e., for example the bearing surfaces and the races of ball and roller bearings. Accordingly, the desired result is achieved only to a very limited degree. In many cases, the lubricant remains entirely within the reservoir and never reaches the bearing location. After a period of time, the lubricant hardens gradually and may even develop crustlike layers which contain abraded metal and other contaminants which further impede any movement of the lubricant in the direction of the bearing or to other locations where lubrication is required. Under those circumstances, the relatively moving parts receive no lubrication at all and make dry metal-to-metal contact leading to rapid deterioration. Furthermore, most lubricants tend to congeal at low temperatures making it very difficult for the lubricant to migrate from the reservoir to the intended point of lubrication.
It is also known in the art to provide positive relubrication by means of grease cups or with a grease injector system which is a very complicated mechanism. This type of relubrication requires constant supervision which is sometimes difficult to attain. Furthermore, it has been shown by actual tests that even though the grease reservoirs may contain sufficient lubricant, only very small amounts of grease are ever available at the points of intended lubrication so that very often the relatively moving parts run dry.